A Segregated, Partially Oxidized, and Compact Ag10 Cluster within an Encapsulating DNA Host

Area of Science:

• Nanomaterials Science
• Biophysical Chemistry
• Spectroscopy

Background:

• Silver clusters can act as optical chromophores within DNA.
• These chromophores exhibit diverse electronic spectra and emission intensities.
• A specific silver cluster demonstrates chameleon-like properties, transforming into different emissive fluorophores.

Purpose of the Study:

• To characterize a specific silver cluster that develops within single-stranded DNA.
• To determine the cluster's size, charge, chirality, and structure.
• To elucidate the complex's overall structure and binding within DNA.

Main Methods:

• Electrospray ionization mass spectrometry (ESI-MS) for cluster size determination.
• Ag L3-edge X-ray absorption near-edge structure (XANES) spectroscopy for cluster charge analysis.
• Circular dichroism (CD) spectroscopy for chirality assessment.
• Ag K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy for structural investigation.

Main Results:

• A stable Ag10 cluster was identified, common across different oligonucleotides.
• The cluster possesses a partial charge of +6 to +6.5, indicating significant oxidation.
• Cluster chirality is dependent on DNA sequence and length, with a binding site of approximately 20 nucleobases.
• EXAFS analysis revealed a core-shell structure with distinct silver-silver coordination environments.

Conclusions:

• A Ag10(+6) cluster forms within a 20-nucleobase DNA binding site.
• The complex features a compact, metallic silver core weakly linked to an outer silver-DNA shell.
• This study provides insights into silver-silver coordination within the cluster core.